This proposal deals with the presteady state kinetics of skeletal and cardiac myosin ATPase, using fluorescent nucleotides, nanosecond fluorescence and stopped-flow techniques. Our interest is focused on the detailed kinetic steps involved in the overall hydrolysis reaction. These studies are expected to provide a basis for a critical examination of the possibility that conformational changes experienced by myosin play a relevant role in the contractile mechanism. BIBLIOGRAPHIC REFERENCES: F. Garland and H. C. Cheung, "Interaction of 1,N6-ethenoadenosine-5'-diphosphate epsilon DP) with Enzymatic Myosin Subfragments: A Fluorescent Probe Study," Biophys. J., 16a, 46 (1976).